The present invention relates to methods and compositions of improving wellbore cleanout treatments.
Subterranean formations containing hydrocarbons are often penetrated by one or more wellbores and acid treated with aqueous acid compositions to stimulate production of hydrocarbons therefrom. In some treatments, the aqueous acid composition is introduced into the wellbore under pressure so that it flows through the pore spaces of the formation and reacts with acid soluble materials contained therein. By doing so, the aqueous acid composition enlarges the pore spaces through which hydrocarbons may flow and be recovered. Such acid treatments also involve pumping an acid into the wellbore through equipment tubulars used during subterranean formation operations (e.g., treating lines, pumping equipment, tubing string, and the like), which also beneficially removes contaminant debris (e.g., scale, mud or cement deposits, corrosion byproducts, and the like) from the internal surfaces of the tubulars. Indeed, the process of removing contaminant debris from equipment tubulars, may be performed even without acid treating the formation.
While acid treating a wellbore in a subterranean formation provides beneficial advantages to hydrocarbon production and equipment maintenance, such treatment may also cause undesirable unconsolidated particulates to remain in the wellbore. For example, the acid may cause mineral dissolution and particulate precipitation (e.g., iron oxide, silica, and the like) from the subterranean formation itself and/or the equipment tubulars. Such unconsolidated particulates may gather in the newly enlarged pore spaces of the formation and effectively negate some or all of the benefits of acid treating the formation. Therefore, acid treatments are generally preceded by cleanout treatments that recirculate the unconsolidated particulates back to the surface and out of the wellbore, and prepare the wellbore and tubulars to receive acidic fluids. Such treatments are often referred to as acid pickling or pickling treatments, and the fluids are often referred to as acid pickling or pickling fluids. Typically, such cleanout treatments use weakly acidic viscous pills containing viscosifiers such as uncrosslinked hydroxyethyl cellulose liner gel pills used for suspending particulates and/or corrosion inhibitors to minimize corrosion to the tubulars during the treatment. Linear gel pills comprise aqueous uncrosslinked polymer solutions. However, such viscous pills often have only moderate to low success rates at capturing and removing unconsolidated particulates. The low success rate may be attributed to an inability to sufficiently suspend the unconsolidated particulates. The viscous pills may additionally reduce permeability in the formation, such as by plugging of the near-wellbore formation pores with particulates due to unwanted fluid leak-off in the formation.
Therefore, a cleanout treatment fluid capable of providing suspension of unconsolidated particulates or fluid loss control may be of benefit to one of ordinary skill in the art.